Immune disorders are characterized by the inappropriate activation of the body's immune defenses. Rather than targeting infectious invaders, the immune response targets and damages the body's own tissues or transplanted tissues. The tissue targeted by the immune system varies with the disorder. For example, in multiple sclerosis, the immune response is directed against the neuronal tissue, while in Crohn's disease the digestive tract is targeted.
Immune disorders affect millions of individuals and include conditions such as asthma, allergic intraocular inflammatory diseases, arthritis, atopic dermatitis, atopic eczema, diabetes, hemolytic anaemia, inflammatory dermatoses, inflammatory bowel or gastrointestinal disorders (e.g., Crohn's disease and ulcerative colitis), multiple sclerosis, myasthenia gravis, pruritis/inflammation, psoriasis, rheumatoid arthritis, cirrhosis, and systemic lupus erythematosus.
A major cellular pathway in the pathogenesis of autoimmunity is the TLR/IRAK1/IRF/IFN pathway. For example, levels of IFNα (type I interferon) are elevated in patients with autoimmune diseases, including systemic lupus erythematosus (SLE), and are central to disease pathogenesis, correlating with autoantibodies and disease development. Recent genetic studies in SLE patients and lupus-prone mice have identified variants in the genes critical for the TLR/IRAK1/IRF/IFN pathways, including TLR7, IRAK1 and IRF5. In addition, several TLR inhibitors are in development for treatment of SLE. Notably, IRAK1 genetic variants have recently been identified in human SLE. IRAK1, a well-established pivotal player in TLRs and inflammation, is located on the X chromosome, which may help account for the fact that SLE is more common in women. Importantly, studies using mouse models, where the IRAK1 gene is removed, have demonstrated a key role for this kinase in the TLR7/9/IRF pathway that produces large quantities of IFNα in response to viral infection. IRAK1 gene deletion prevents TLR dependent activation of IRF5/7 in pDCs, the immune cells responsible for IFNα production. Significantly, autoantibody complexes obtained from SLE patients contain DNA and RNA and are taken up by pDCs to activate TLR7 and TLR9 leading to secretion of cytokines and IFNα. Moreover, TLR activation is known to inhibit activity of glucocorticoids, a frontline drug class used to treat SLE. Although IRAK1 activity is regulated by phosphorylation upon TLR activation, little is known about whether it is subject to further control after phosphorylation and whether such regulation has any role in SLE.
The prevalence of asthma is increasing in the developed world, but the underlying mechanisms are not fully understood, and therapeutic modalities remain limited. Asthma is a chronic inflammatory disease of the airways that is induced by overexpression of multiple proinflammatory genes regulated by various signal pathways in response to exposure to any of numerous allergens, including Toll-like receptor/interleukin-1 receptor (TLR/IL-1R) signaling activated by house dust mite (HDM) allergens and IL-33, respectively. A major regulatory mechanism in these signal pathways and gene activation is Pro-directed phosphorylation (pSer/Thr-Pro), but until recently little was known about whether and how they are regulated following phosphorylation.
Current treatment regimens for immune disorders typically rely on immunosuppressive agents. However, the effectiveness of these agents can vary and their use is often accompanied by adverse side effects. Thus, improved therapeutic agents and methods for the treatment of autoimmune disorders are needed.
In addition, drug addiction affects millions of individuals worldwide. The prevalence of cocaine addiction, for example, is estimated at over one million persons in the United States alone. Dopamine receptor signaling is understood to play a major role in addiction to drugs such as cocaine known to elicit dopamine responses. Dopamine induction is coupled to the phosphorylation of glutamate receptor protein mGluR5, which in turn potentiates NMDA receptor-mediated synaptic plasticity and thus cocaine-induced sensation. MAP Kinase phosphorylates mGluR5 where it binds the adaptor protein Homer and in so doing is thought to create a binding site for proteins that catalyze cis-trans isomerization of a phosphorylated serine-proline bond (pSer/Pro). Despite this recognition, there are presently no FDA-approved medications to treat cocaine addiction. Accordingly, there is a need to identify and develop therapeutic agents for the treatment of cocaine addiction.
The increased number of cancer cases reported in the United States, and, indeed, around the world, is also a significant concern. There are currently only a handful of detection and treatment methods available for some specific types of cancer, and these provide no absolute guarantee of success. In order to be most effective, these treatments require not only an early detection of the malignancy, but a reliable assessment of the severity of the malignancy.
It is apparent that the complex process of tumor development and growth must involve multiple gene products. It is therefore important to define the role of specific genes involved in tumor development and growth and identify those genes and gene products that can serve as targets for the diagnosis, prevention, and treatment of cancers.
In the realm of cancer therapy, it often happens that a therapeutic agent that is initially effective for a given patient becomes, over time, ineffective or less effective for that patient. The very same therapeutic agent may continue to be effective over a long period of time for a different patient. Further, a therapeutic agent that is effective, at least initially, for some patients can be completely ineffective from the outset or even harmful for other patients. Accordingly, it would be useful to identify genes and/or gene products that represent prognostic genes with respect to a given therapeutic agent or class of therapeutic agents. It then may be possible to determine which patients will benefit from a particular therapeutic regimen and, importantly, determine when, if ever, the therapeutic regime begins to lose its effectiveness for a given patient. The ability to make such reasoned predictions would make it possible to discontinue a therapeutic regime that was losing its effectiveness well before its loss of effectiveness becomes apparent by conventional measures.
Recent advances in the understanding of molecular mechanisms of oncogenesis have led to exciting new drugs that target specific molecular pathways. These drugs have transformed cancer treatments, especially for those caused by some specific oncogenic events, such as Herceptin for breast cancer, caused by HER2/Neu, and Gleevec® for chronic myelogenous leukemia caused by Bcr-Abl. However, it has been increasingly evident that, in many individual tumors, there are a large number of mutated genes that disrupt multiple interactive and/or redundant pathways. Thus, intervening in a single pathway may not be effective. Furthermore, cancer resistance to molecularly targeted drugs can develop through secondary target mutation or compensatory activation of alternative pathways, so-called “oncogenic switching.” Thus, a major challenge remains how to simultaneously inhibit multiple oncogenic pathways either using a combination of multiple drugs, with each acting on a specific pathway, or using a single drug that concurrently blocks multiple pathways.
Cancer stem-like cells (CSCs) or tumor-initiating cells (TICs) have been hypothesized to retain the capacity of self-renewal and regeneration of the bulk of a heterogeneous tumor comprised of CSCs and non-stem cells. CSCs have important implications for understanding the molecular mechanisms of cancer progression and developing novel targets for cancer therapeutics because they are thought to be responsible for tumor initiation, progression, metastasis, relapse and drug resistance. A variety of regulators of breast cancer stem-like cells (BCSCs), notably transcription factors including Zeb1 and β-catenin, and miRNAs, have recently been identified. These modulators of transcription and/or translation are further regulated by upstream signaling pathways. For example, Erk signaling has been shown to regulate BCSCs by increasing transcription of Zeb1 and nuclear accumulation of unphosphorylated (active) β-catenin. However, regulatory pathways upstream of Erk signaling that regulates BCSCs are still not fully elucidated.
Among the small GTPase superfamily, Ras has been shown to induce epithelial mesenchymal transition (EMT) and confer CSC traits to breast cells in vitro and in vivo, while the Rho family GTPase Rac1 is involved in the maintenance and tumorigenicity of CSCs in non-small cell lung adenocarcinoma and glioma and is also required for intestinal progenitor cell proliferation and LGR5+ intestinal stem cell expansion. Deletion of Rac1 in adult mouse epidermis stimulated stem cells to divide and undergo terminal differentiation. However, the roles of other GTPase family members in CSCs in solid tumors or adult stem cells are yet to be elucidated. For example, Rab2A, a small GTPase mainly localized to the ER-Golgi intermediate compartment (ERGIC), is essential for membrane trafficking between the ER and Golgi apparatus but has no known function in cancer or CSCs. As disclosed herein, we have unexpectedly found that Rab2A is a Pin1 transcriptional target that is activated via its gene amplification or mutation or Pin1 overexpression in breast cancer and promotes BCSC expansion in vitro and in vivo as well as in human primary normal and cancerous breast tissues. Mechanistically, Rab2A directly binds to Erk1/2 via a docking motif that is also used by an Erk1/2 phosphatase, MKP3 (MAP kinase phosphatase 3) to prevent Erk1/2 from being dephosphorylated/inactivated, leading to activation of the known BCSC regulators Zeb1 and β-catenin. We further describe a tight association of Rab2A overexpression with β-catenin or Zeb1 downstream target expression in human breast cancer tissues as well as with poor outcome of breast cancer patients, especially in the most common subtypes, as defined by HER2-negative or non-triple-negative breast cancer. Thus, the Pin1/Rab2A/Erk axis drives BCSC expansion and tumorigenicity, contributing to high mortality in patients. Similarly, Pin1 has also been identified as a critical regulator acting downstream of miR200c.
These and other results disclosed herein suggest that Pin1 inhibitors may have a major impact on treating cancers, especially aggressive and/or drug-resistant cancers. A common and central signaling mechanism in many oncogenic pathways is proline (Pro)-directed phosphorylation (pSer/Thr-Pro). Proline adopts cis and trans conformations, the isomerization of which is catalyzed by prolyl isomerases (PPIases) including Pin1. Phosphorylation on serine/threonine-proline motifs restrains cis/trans prolyl isomerization, and also creates a binding site for the essential protein Pin1. Pin1 binds and regulates the activity of a defined subset of phosphoproteins, as well as participating in the timing of mitotic progression. Both structural and functional analyses have indicated that Pin1 contains a phosphoserine/threonine-binding module that binds phosphoproteins, and a catalytic activity that specifically isomerizes the phosphorylated phosphoserinelthreonine-proline. Both of these Pin1 activities are essential for Pin1 to carry out its function in vivo.
Pin1 has been implicated in autoimmune diseases and conditions such as SLE and asthma and in drug addiction pathways. Further, we and others have shown that Pin1 is prevalently overexpressed in human cancers and that high Pin1 marker levels correlate with poor clinical outcome in many cancers. In contrast, the Pin1 polymorphism that reduces Pin1 expression is associated with reduced cancer risk in humans. Significantly, Pin1 activates at least 32 oncogenes/growth enhancers, including β-catenin, cyclin D1, NF-κB, c-Jun, c-fos, AKT, A1B1, HER2/Neu, MC1-1, Notch, Raf-1, Stat3, c-Myb, Hbx, Tax, and v-rel, and also inactivates at least 19 tumor suppressors/growth inhibitors, including PML, SMRT, FOXOs, RARα, and Smad (FIG. 1). Whereas Pin1 overexpression causes cell transformation and tumorigenesis, Pin1 knockdown inhibits cancer cell growth in cell cultures and mice. Pin1-null mice are highly resistant to tumorigenesis induced either by oncogenes such as activated Ras or HER2/Neu, or tumor suppressors such as p53. Thus, Pin1 inhibitors may have the desirable property to suppress numerous oncogenic pathways simultaneously for treating cancers, especially those aggressive and/or drug-resistant cancers. Potent and selective Pin1 inhibitors having low toxicity, high cell permeability, and long half-lives in the body are particularly desirable.
Pin1 is highly conserved and contains active sites including a protein-interacting module, called the WW domain, and a catalytically active peptidyl-prolyl isomerase (PPIase) portion, each of which include at least one binding pocket. Pin1 is structurally and functionally distinct from members of two other well-characterized families of PPIases, the cyclophilins and the FKBPs. PPIases are ubiquitous enzymes that catalyze the typically slow prolyl isomerization of proteins, allowing relaxation of local energetically unfavorable conformational states. Phosphorylation on Ser/Thr residues immediately preceding Pro not only alters the prolyl isomerization rate, but also creates a binding site for the WW domain of Pin1. The WW domain acts as a novel phosphoserine-binding module targeting Pin1 to a highly conserved subset of phosphoproteins. Furthermore, Pin1 displays a unique phosphorylation-dependent PPIase that specifically isomerizes phosphorylated Ser/Thr-Pro bonds and regulates the function of phosphoproteins. The cis-trans isomerization of certain pSer/Thr-Pro motifs can be detected by cis- and trans-specific antibodies.
Taken together, these results indicate that the Pin1 subfamily of enzymes is a diagnostic and therapeutic target for diseases associated with signal pathways involving Pro-directed phosphorylation and characterized by uncontrolled cell proliferation, primarily malignancies.
We have surprisingly found that an approved anticancer reagent with an unknown mechanism, all-trans retinoic acid (ATRA), potently and reversibly binds and inhibits and ultimately induces degradation of active Pin1. The use of all-trans retinoic acid (ATRA) to treat acute promyelocytic leukemia (APL) is described as the first example of targeted therapy in human cancer. ATRA induces leukemia cell differentiation by activating RARα or the oncogene PML/RARα-dependent transcription and induces degradation of PML/RARα. However, the mechanism by which ATRA mediates these anticancer effects is unknown. Though RARα and PML have been described as Pin1 substrates, the link between ATRA and Pin1 is poorly understood. The establishment of the mechanism of interaction between ATRA and Pin1 could facilitate the development and identification of selective Pin1 inhibitors with low toxicity, high cell permeability, and long half-lives for use in the treatment of proliferative and other disorders. Accordingly, there is a need for an improved understanding of the binding interaction between ATRA and Pin1.